Thrice previous, the Flash of Earth-One faced his most persistent and deadliest foe, Eobard Thawne... also known as Professor Zoom or the Reverse-Flash. The villain gained that last alias by retrieving a spare Flash uniform in a time capsule, and extracting from it the residual speedforce of its former owner, thus gaining superspeed himself. Only he sought to use such abilities for crime instead of justice, in both his own 24th century and in the Flash's 20th century. Eventually, Thawne realized he was missing out on the "good life" of his arch-enemy, and so traded places with the Flash. With the Monarch of Motion now trapped in a futuristic prison, the Menace of Motion changed his appearence to that of Flash's alter ego, Barry Allen, and absorbed recent memories of Barry in order to assume both his civilian and costumed identities. Finally, he realized what a gem Allen had in his fiancee, Iris West... and so intended to marry her.
However, the Flash found away out of Zoom's prison, and returned to the 20th century to face off versus the Professor. Meanwhile, Thawne had now met Iris at the altar to marry her in front of her friends and family. However, the Flash arrived and grapped the groom, as both adversaries left behind a stunned audience. Zoom had a device in his possession that animated objects to bend to his will, which he used versus the Flash, yet this was not enough for him to defeat the Fastest Man Alive. Barry knew how to draw out Eobard, by chasing after his foe and luring him to a body of water... where Zoom sunk into as he was not yet skilled in running across water. When the authorities from his native time retrieved the Professor, the real Barry Allen was able to return to the wedding gathering and complete his vows.
Interestingly, at this marital event, there was a notable absence... Jay Garrick aka the Flash of Earth-Two. Where was he at this time? Well, at approximately this same time, Jay and his fellow Justice Society of America allies journeyed to Earth-A instead of Earth-One... a fraudulent world created by that world's Johnny Thunder. Okay, the Earth-A incident occured on September 1965 instead of November 1966 when the wedding took place, however given the different vibratory frequencies between Earths this would be around the same timeframe and hence the reason Jay wasn't present to see his best friend Barry get married... and was thus unable to aid him versus Zoom. But he would aid him later on, years later into Barry and Iris' new life together, which had its share of twists and turns that would test the depth of their love for one another.